Urban Runoff or 'storm drain pollution' is one of the leading causes of water pollution in this country. Urban areas contain up to 90 percent hard surfaces such as rooftops and pavement where water collects and quickly runs off. Urban Runoff is difficult to prevent because it is nonpoint pollution. That is, instead of originating from a single-point source, such as a factory or sewage treatment plant, the sources of urban runoff are spread throughout an urban area. Such sources include yards, sidewalks, streets, construction sites and parking lots. Any deposits of oil, grease, pesticides, herbicides, soil, pet droppings, etc. in these areas are flushed by rainwater and other means down the storm drains and directly into a river or bay (Source: Monterey National Marine Sanctuary). The EPA estimates that 70% of water pollution comes from stormwater and sewer discharge. This increase in flow can have impacts on sediment, riparian plant life, and erosion. (Source Coastal Watershed Council).